Yingluck, who says the charges are politically motivated, is believed to have fled the country last month before the court session at which the verdict initially was to have been delivered.
Yingluck was due to hear the verdict on August 25, but failed to show up, surprising hundreds of supporters who had gathered at the court.
Yingluck, who inherited the leadership of Thaksin's political machine and was elected prime minister in 2011, became a proxy target for his enemies as well.
The grounds of the ruling was that Yingluck had given an interview in which she said trades had been conducted between governments.
"The court found that the defendant is guilty as charged.the court has sentenced her to five years in prison and the court also unanimously agreed that the sentence will not be suspended", the judge said. "Therefore, the action of the accused is considered negligence of duty", it said.
Uber Ordered To Leave London - Company Appeals
The initial background checks were carried out by a third party but TfL deemed them inadequate following a review. CEO Dara Khosrowshahi himself apologized and states that the company is open to change.
50-year-old Shinawatra was found guilty of causing losses to the state amounting to €6.8 billion by issuing subsidies for growing rice.
Ms Yingluck is thought to be in Dubai where her brother, former Prime Minister Thaksin Shinawatra, lives in self-imposed exile avoiding a 2008 sentence for corruption.
Thitinan Pongsudhirak, director of the Institute of Security and International Studies at Chulalongkorn University, said the Puea Thai Party was now "rudderless". "I do not know".
The generals have promised an eventual return to democracy but the date for elections keeps slipping, as they extend their clampdown on dissent.